[HarfBuzz] Tai Tham Shaping Question #2 : MEDIAL RA

[Andrew Cunningham]

Hi Behdad,

Will the approach of using DFLT script work with a multi a multiscript
font? I.e. if I need to support Arabic (Jawi), Western Cham and Khmer?

And if I need to support reordering and ligatures DFLT will be ok?

Are all OT features supported by DFLT or only some?

Andrew
On 10/12/2012 6:42 PM, "Behdad Esfahbod" <behdad at behdad.org> wrote:

> On 12-11-14 08:36 PM, Theppitak Karoonboonyanan wrote:
> > On Thu, Nov 15, 2012 at 2:53 AM, Behdad Esfahbod <behdad at behdad.org>
> wrote:
> >> On 12-11-14 01:15 AM, Theppitak Karoonboonyanan wrote:
> >>> On Tue, Nov 13, 2012 at 4:45 AM, Behdad Esfahbod <behdad at behdad.org>
> wrote:
> >>>> Ed!
> >>>>
> >>>> There's no way we can fix these without a font!  Just send the font
> first
> >>>> already :).  Jonathan and I are having yet another HarfBuzz Hackfest
> week this
> >>>> week and like to address the remaining issues for "Tai *" scripts :).
> >>>
> >>> While waiting for Ed, you may try Khottabun font for Lao/Esaan Tham
> script,
> >>> another Tai Tham variation used in Lao and northeastern Thailand:
> >>>
> >>>  http://linux.thai.net/~thep/esaan-scripts/fonts/Khottabun.ttf
> >>>
> >>> The font, however, has provided all the reordering rules in GSUB, so
> that it
> >>> can still display on absence of rendering engine preprocessing. It may
> not be
> >>> good for your testing, but you can get some idea of the requirements
> from it.
> >>
> >> Humm.  Then it's not interesting indeed.  Even worse, those rules may
> conflict
> >> with the engine processing :|.
> >
> > I know. That's why I said it might not be good for your testing. Just
> hope to
> > provide some sample for comparison using another system without the
> > processing.
>
> Our current recommendation is that if your font does NOT rely on the engine
> reordering, it's best to use the DFLT script.  In HarfBuzz we use that
> clue to
> decide whether to use the Indic shaper or the generic shaper.  In some
> cases,
> using a font designed for the generic shaper with the Indic shaper can
> produce
> inferior results.
>
>
> > And I hope the sample text in the test page could still be some help.
> >
> > One common case that's still missing in the test page, though, is "ᨯᩪᩕᩣ",
> > where MEDIAL RA has to be shifted left by two positions.
> > The sequence is:
> >
> >   U+1A2F TAI THAM LETTER DA
> >   U+1A6A TAI THAM VOWEL SIGN UU
> >   U+1A55 TAI THAM CONSONANT SIGN MEDIAL RA
> >   U+1A63 TAI THAM VOWEL SIGN AA
> >
> > And the rendered sequence should be:
> >
> >   U+1A55 TAI THAM CONSONANT SIGN MEDIAL RA
> >   U+1A2F TAI THAM LETTER DA
> >   U+1A6A TAI THAM VOWEL SIGN UU
> >   U+1A63 TAI THAM VOWEL SIGN AA
>
> Right.  This behavior is like the medial Ra in Myanmar, so should be fine
> when
> we implement that.
>
>
> > Regarding the font development, since we want to make progress on other
> > parts of the language support, such as input method, adding GSUB is all
> > we can do while the rendering engine supports are still lacking.
> >
> > Once HarfBuzz supports it, I'll remove the rules and distribute two
> > different versions of the font, one for HarfBuzz, the other for other
> > engines.
>
> Or just ship one that has both a DFLT table, and a non-DFLT table.
>
>
> > Regards,
> >
>
> --
> behdad
> http://behdad.org/
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>
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